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United States Patent |
6,082,938
|
Fink
|
July 4, 2000
|
Integral frame and method of manufacture
Abstract
A unitary frame structure is disclosed as well as a method of manufacturing
the same. The unitary frame structure typically includes a first beam, a
second beam adjoining the first beam, and a cross member adjoining the
first beam and the second beam. Significantly, each of the first beam,
second beam and cross beams have a Z shaped cross-sectional structure
formed by a first flange that is adjacent a substantially vertical portion
further shaped with a second lip adjacent an opposite end of the first
lip. This Z cross section is formed by machining a unitary pallet in a
first vertical direction to form the first lip, flipping the pallet and
then machining in a substantially vertical portion in the opposite second
vertical direction to form the second lip on an opposite side of the
substantially web section only. Placed periodically along the rib sections
are stiffening elements formed during the machining operation.
Inventors:
|
Fink; Carl Joseph (Keller, TX)
|
Assignee:
|
Lockheed Martin Corporation (Bethesda, MD)
|
Appl. No.:
|
207285 |
Filed:
|
December 8, 1998 |
Current U.S. Class: |
409/132; 409/131 |
Intern'l Class: |
B23C 009/00 |
Field of Search: |
409/132
29/897.312
|
References Cited
U.S. Patent Documents
3749625 | Jul., 1973 | Berg.
| |
4260304 | Apr., 1981 | Jacobi.
| |
5079821 | Jan., 1992 | Parsons.
| |
5273806 | Dec., 1993 | Lockshaw et al.
| |
5487930 | Jan., 1996 | Lockshaw et al.
| |
5508085 | Apr., 1996 | Lockshaw et al.
| |
5836729 | Nov., 1998 | Fink | 409/132.
|
Foreign Patent Documents |
671941 | Jul., 1979 | SU.
| |
733877 | May., 1980 | SU.
| |
1227372 | Apr., 1986 | SU.
| |
1227373 | Apr., 1986 | SU.
| |
1404201 | Jun., 1988 | SU.
| |
Primary Examiner: Gerrity; Stephen F.
Assistant Examiner: Wilson; Adrian M.
Attorney, Agent or Firm: Felsman Bradley Vaden Gunter & Dillon, LLP, Bradley; James E.
Claims
I claim:
1. A method manufacturing a unitary frame structure comprising the steps
of:
with a machining element, machining a unitary pallet in a first vertical
direction, thereby forming a first lip and a first substantially vertical
portion;
moving said unitary pallet in a horizontal direction relative to said
machining element;
selectively tilting said machining element in said vertical direction so as
to form stiffening elements along said first lip in said first
substantially vertical portion;
machining said unitary pallet in a second vertical direction parallel to
said first vertical direction to form a second lip in a second
substantially vertical portion, wherein said lips and said vertical
portions form a beam with a Z cross-section;
moving said machining element relative to said vertical pallet in a
horizontal direction; and
moving said machining element relative to said second vertical direction in
selected locations thereby forming stiffening elements along said second
lip in said second substantially vertical portion.
2. The method according to claim 1, wherein said stiffening elements have a
beveled surface skewed to said vertical portions connecting one of said
lips with an adjacent vertical portion.
3. The method according to claim 1 further comprising the step of:
moving said unitary pallet in selected horizontal directions relative to
said machining element, thereby forming adjoining rib sections to form a
unitary frame structure.
4. The method according to claim 1 further comprising the step of:
removing any extraneous blocks of material not part of said Z
cross-sections.
5. The method according to claim 1, wherein said unitary pallet comprises
aluminum.
Description
TECHNICAL FIELD
The present invention relates generally to an integrated frame structure
and a method of manufacture. More particularly, the present invention
relates to a highly integrated frame manufactured substantially from a
single block of material having a high degree of strength with a minimal
amount of assembly.
BACKGROUND ART
Frame understructures used in environments subject to great physical stress
are well-known in the art. For example, one type frame understructure is
used in the vertical tail section of military aircraft such as, for
example, the F-16 fighter jet manufactured by Lockheed. The vertical tail
structure typically consists of numerically controlled (NC) machined
C-channel spars and ribs mechanically fastened together. The outboard
panel of the aileron is a bonded assembly, typically comprising
graphite/epoxy skins bonded to aluminum honeycombed core and mechanically
fastened to the NC machined aluminum periphery structure. While this
bonded assembly is considered to be one of the lightest possible structure
configurations, there are substantial manufacturing risks associated with
bonding dissimilar metals and materials as well as the normal risks
associated with the bonding assembly.
Milling a frame from a single block of metal is also well-known in the art.
Unfortunately, these previously designed or manufactured substantially
integrated understructures required additional supports afterward or
lacked strong rigidity necessary for high stress environments. Further,
these prior solutions suffered from the drawbacks of having high waste
byproducts as well as long lead times for manufacture and development and
high expense relative to previously available frame structures.
Accordingly, there is a need for an improved method of manufacturing highly
integrated understructures that overcome the prior problems of undue
waste, high lead time, and great expense in design preparation and
manufacture.
DISCLOSURE OF THE INVENTION
According to the present invention, a unitary frame structure is disclosed
as well as a method of manufacturing the same. The unitary frame structure
typically includes a first beam, a second beam adjoining the first beam,
and a cross member adjoining the first beam and the second beam.
Significantly, each of the first rib, second rib and cross member have a Z
shaped cross-sectional structure formed by a first lip or flange that is
adjacent a substantially vertical portion further shaped with a second lip
or flange adjacent an opposite end of the first lip or flange. This Z
cross section is formed by machining a unitary pallet in a first vertical
direction to form the first flange, then flipping the pallet, and then
machining in a substantially vertical direction in the opposite second
vertical direction to form the second flange on an opposite side of the
substantially vertical section only. Placed periodically along the beam
sections are stiffening elements formed during the machining operation.
The stiffening elements are formed to resist bending in a principle
bending direction along the Z section. The stiffening elements typically
have a substantially flat plane that is skewed to the vertical portions or
webs thereby connecting one of the flanges to the adjacent vertical
portion or web. These stiffening elements are typically placed
back-to-back on adjacent sides on the same Z cross section.
The method to manufacture the unitary frame follows the following steps.
First, the unitary pallet is machined in a first vertical direction to
form a first flange and a first side of a web. The pallet is then moved in
a horizontal direction relative to the machine element. Then the machine
element is selectively tilted in the vertical direction so as to form
stiffening elements along the first lip flange. Next, the machining of the
unitary pallet is performed in a second vertical direction parallel to the
first vertical direction to form a second flange on a second side of the
substantially vertical portion. These machine operations form the Z cross
section. Just as was done in the first vertical direction, the machine
element is moved relative to the vertical pallet in a horizontal direction
in the second vertical direction to form stiffening elements on the
reverse side. Typically, the stiffening elements are adjacent one another
at the same Z section. The beveled surface of the stiffening elements is
skewed to the vertical portions thereby connecting one of the lips with
the adjacent vertical portion. Lastly, any extraneous blocks of material
not part of the Z cross sections are removed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a vertical tail understructure;
FIG. 2 is a cutaway side view of the structure in the direction shown in
FIG. 1;
FIG. 3 depicts a top plan view of a first side being milled;
FIG. 4 illustrates selected sections being completely processed and other
sections remaining to be processed;
FIG. 5 is a top plan view of the reverse of the structure where several
blocks have been removed with several other block having yet to be removed
by the cutting of the tab sections; and
FIG. 6 illustrates a top plan view of the frame structure after completion.
BEST MODE FOR CARRYING OUT THE INVENTION
A one-piece machined understructure for use in high stress environments has
been developed. This novel integrated structure eliminates traditional
bonded assembly practices as well as reduces the weight of a built-up
understructure previously used in such high stress environments. For
purposes of illustrating the advantages of the novel design and method of
manufacturing an understructure 10, one embodiment of the invention is
disclosed in FIG. 1. The invention is a vertical tail understructure
typically used in a military jet aircraft, for example an F-16. Other uses
for the method and manufacture as well as the design aspects of the
understructure 10 will become readily apparent to those skilled in the art
and is not intended to be limited to merely being a vertical tail
understructure for use in a jet aircraft.
As applied to a control surface, the novel method of the present invention
result in an integrated understructure 10 that replace four machined
details and several core details of integrated understructure 10 with a
single multi-ribbed machined part. A substantial portion of understructure
10 is, instead, machined from just two sides of a single billet of
material including all of interior ribs or beams 12.
By contrast, the previous vertical tail understructure manufactured
according to the prior manufacturing technology required six internal
beams and three internal spars, comprising forty detailed parts in all for
a comparable design. The structure 10 is milled from a single machine
detail.
Interior ribs or beams 12 are designed to have a Z-cross section which is
defined by a first lip 13a, a substantially vertical portion 13b, and a
second lip 13c. Additionally, stiffeners 14 are periodically spaced along
each beam 12. Stiffeners 14 are included to provide web buckling
resistance and flange support for fuel pressure. Fuel flow holes and
routing holes for tubing are added to the webs secondarily after the part
is machined.
FIG. 2 is a cutaway side view of structure 10 in the direction shown in
FIG. 1. In this view, the Z structure 16 is most evident as well as the
machining of the stiffeners. A milling bit 18 mills substantially
vertically while forming the Z section beams and then is tilted sideways
so as to provide the stiffener sections to the beam. Once the first side
is completed, then the entire structure 10 is rotated 180 degrees to mill
the second side.
FIG. 3 depicts a top plan view of a first side being milled while FIG. 4
illustrates selected sections of the second side being completely
processed, with other sections still remaining to be processed. During the
milling process, tabs 20 are maintained between the extraneous material 22
to be removed and the frame structure 10. At a later stage, upon
completion of the milling process, the tabs are cut and then filed, thus
removing the extraneous material. The extraneous material, depending on
the size, may be used for other, smaller parts for other applications,
thus reducing material waste.
FIG. 5 is a top plan view of the second side of structure 10 where several
blocks 22 have been removed with several other blocks 22 having yet to be
removed by the cutting of tabs 20. The remaining portion has yet to be
milled. Typically, however, both sides are milled before any blocks 22 are
removed and this drawing is provided for illustrative purposes. FIG. 6
illustrates a top plan view of frame structure 10 after completion,
including the filing of the tabs 20.
The finished integrated understructure 10, illustrated in FIG. 6, achieves
substantial cost reduction over the prior method for several reasons. One
reason is that the imaginary drawing count is reduced by thirty drawings
(for an entire aircraft) as compared to a part by part assembly that was
previously required. Additionally, the detailed part count is reduced by
approximately eighty fewer details, which also leads to a reduced count in
fasteners required. Since a single billet of material is used that
requires substantially no assembly after being machined, significant
tooling reduction is also achieved. Additionally, since the process is
machined, manual labor necessary to assemble the understructure is
reduced.
The method to manufacture the unitary frame structure 10 follows the
following steps. First, the unitary pallet is machined in a first vertical
direction 24 to form a first flange 13a and a first substantially vertical
web portion 13b. The pallet is then moved in a horizontal direction 26
relative to the machine element and then the machine element is
selectively tilted in the vertical direction so as to form stiffening
elements 14 along the first flange 13a in the substantially vertical web
portion 13b. Next, the machining of the unitary pallet is performed in a
second vertical direction 28 parallel to the first vertical direction 24
to form a second flange 13c in a second substantially vertical portion.
These resulting machine operations form the Z cross section or Z structure
16. Just as was done on the first vertical direction 24, the machine
element is moved relative to the vertical pallet in a horizontal direction
26 in the second vertical direction 28 to form stiffening elements 14 on
the reverse side. This step may be accomplished by flipping the pallet.
Typically, the stiffening elements 14 are adjacent one another at the same
Z section. The beveled surface of the stiffening elements 14 is skewed to
the vertical portions, thereby connecting one of the flanges 13a or 13c
with the adjacent vertical web portion 13b. Lastly, any extraneous blocks
22 of material not part of the Z cross sections are removed.
In this application, there are thirty fewer drawings to prepare, check,
release and maintain, as well as significantly fewer detail parts to
procure, receive and stock over the previous method of manufacture. Entire
major tools such as bond forms, are eliminated with the change to the
integrated understructure. The inclusion of tooling tabs on the
understructure and skins further reduces the tooling required, which leads
to a shift from a multiple tool assembly process to a bench operation.
Further, assembly time is reduced as the understructure is already
assembled as machined, and there are no mismatches between spar flanges
and rib flanges to be shimmed or adjusted.
Yet another significant benefit of the application of the integrated
understructure to the control surfaces is the elimination of the bonded
assemblies and their associated risks. To minimize weight and maximize
control surface effectiveness, previously used bonded assemblies
techniques utilized graphite/epoxy skins and aluminum periphery spars.
This construction is identical to the F-16 rudder. While lightweight, the
concept is unpredictable from a producability standpoint. The dissimilar
coefficients of thermal expansion of the spar and skins almost guarantee
that the part will warp during the bonding process as the part cools.
After many attempts, the aluminum spar in the F-16 rudder was pre-warped
in the bond to counter this phenomena, allowing the spar to warp to a
"straight" position during bonding. In most program schedules, there is
not sufficient time to do such a trial and error approach.
The use of the integrated machined understructure in lieu of bonded
assemblies provides additional savings after assembly. In the case of the
bonded assembly, each assembly must have a full non-destructive inspection
(NDI), possibly including x-rays, to determine completeness of the bond.
Further, once in service, the bonded assembly always has the risk of core
corrosion, especially in a high humidity environment. The integrated
understructure component eliminates the need for the post assembly NDI and
there is no chance for core corrosion.
The large, producible, lightweight one-piece machined understructure uses a
Z section that allows for easy machining from two sides. Further,
continuous spar flanges allow for stiffness in principle bending
directions while the Z flanges allow for thin gauges of webs and flanges
not otherwise cost-effectively achievable on conventional parts.
While the invention has been shown in only one of its forms, it should be
apparent to those skilled in the art that it is not so limited, but is
susceptible to various changes without departing from the scope of the
invention.
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